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美国生物学课堂录像-2
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这和1是连起来的。 http://www.divshare.com/download/843680-300 [ Last edited by whyerect on 2007-6-11 at 06:06 ] |
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4楼2007-05-28 04:24:47
2楼2007-04-05 16:20:19
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这是文本内容 lack information and only later journey evolution of life from this planet. When that later was we can tell but it could've been 100 or 200 million years later. * for talking about the origin of life as between 3.3 and 3.5 billion years ago, we can really localize it in time. Very well, but only later, did DNA be, um, was DNA assign the job of storing in the stable flashing genetic information? And as a consequence, we come to realize as well here's another discovery, which is that all the catalysts that we are going to talk about today, the * as we call them. Modern, almost all modren day * are proteins and we talked about them briefly before. But over the last 15 years, 20 years, there has been a discovery, the certain RNA molecules also possess the ability to catalyse certain kinds of reactions. Um, when I was taking biochemistry, if you, if somebody would have told me that I would have, I would have called the Psychi* course. Um, because that was such an outlinedish idea. How can an RNA molecule catalysed by a chemical reaction? It doesn't have all the * groups. There were needs to creat the catalytic sites for reactions. But we now realize on the basis of research which actually let the Nobel Prize be awarded about five years ago that RNA molecules are able to catalyse certain kinds of reactions. And that begins to give us an insight into how life originated on this planet. Because RNA molecules may have stored genetic information as I said before. RNA molecules or their precursors like ATP may have been the currency for storing a high-energy bombs as it's indicated here. And RNA molecules may have been the first * to catalyse many of the reactions in the most * life forms, the first,um,existed on this planet. And therefore what I'm saying is that as life developed in the first 100 or 200 million years,who knows how long it took, gradually DNA took over the job to store information from RNA, and gradually proteins took over the job of, um, mediating catalysis of acting its * to taking the job over from RNA molecules. Today there are certain vestigial biochemical reactions which we believe are relics, echos of the beginning of life on earth, which are still mediated by RNA catalysts. We think that they are threw back to the very early steps, maybe even in piece of, you know, life form where RNA was * with a task of acting its catalyst. We're going to focus a lot today on a whole issue of biochemical reactions and the issue of energy. And this gets us into the realization that there really are 2 kinds of clhemical reactions. Some of you may have * learnt this a long time ago. Either actual * reactions that release energy that produce energy as they produced, oh, as they proceeded or conversely under * reactions which, um, require an investment of energy in order to move forward. So here obviously for this is, is this a high-energy state? And we are talking about the free energy of the system which is one way to depict in thermal dynamic language. How much energy is in a molecule? If we go from a high-energy state to a low-energy state, then what we can draw like this. And we can realize that in order to conserve energy, the energy that was inherent to this molecule. The high potential energy is released as this ball or this molecule rolls down the hill and therefore the reaction yields energy, its actual * conversely. If we want this energy to proceed, we need to invest, excuse me, if we want this reaction to proceed, we need invest free energy in order to make it happen. The free energy happens to be more often, not in the form of chemical bombs. IE energy that can be invested, for example, by taking advantage of potential energy stored this fastful diaster, in this fastful, a fastful linkages indicated right here. Here, by the way, * model of ATP just for your, for your information. That's a way would actually look into life. And this is the way we actually draw it. Now having sat there, if we look at the free energy, a profile of various biochemical changes, then we can dipct them, once again, in this very *matic way here. And by the way, free energy is called G, the Gibbs Free Energy after Gesale Gibbs who was a thermal dynamic wins in the 19th century * |
3楼2007-04-05 17:30:02
